Managing communications between a mobile user employing a wireless user equipment device (UE) and wireless base stations continues to be a challenge in part due to the mobility of the UE. Standards for wireless technologies including 3GPP LTE are continually evolving in order to address needs for higher data transmission efficiency and spectrum utilization efficiency, in particular in the context of a mobile UE.
In one example, in order to further improve the rate of an edge user and the overall performance of a system, the coordinated multipoint transmission (CoMP) technology has been widely considered by the third generation partner project (3GPP) for incorporation into the architecture of standards, such as LTE-A (see 3GPP TS 36.213, Technical Specification Release 10, June 2011, 3rd generation Partnership Project). CoMP, which was designed to facilitate communications with edge users, involves coordinated transmission and reception of data for one or more users through geographically separate transmission points (TP), thereby improving the transmission efficiency and performance at the edge of a cell. The architecture of CoMP differs from a network architecture treated in previous LTE releases in that there are a plurality of geographically separate transmission points serving a user in the CoMP architecture, as compared to a traditional cellular network architecture of LTE (release 8a) where a central or edge user is served only by a cell where the central or edge user is located. In the traditional architecture, only a base station (also designated as evolved NodeB, or eNodeB) serving the user receives uplink data of the user in the uplink path, while in the CoMP architecture, multiple transmission points receive the uplink data from the user during uplink transmission.
In CoMP, among coordinated transmission cells, the cells serving concurrently an individual UE form a cooperating set including a primary cell responsible for tasks of resource scheduling and allocation, coordinated data processing, etc., and one or more cooperative cells responsible for only the process of transmitting and receiving data.
In particular, several scenarios have been developed for possible implementation of CoMP in LTE standards. Among these are scenario 4, in which a heterogeneous network includes low power remote radio heads (RRH) within a macrocell coverage, and where the transmission/reception points created by the RRHs have a same cell ID as the macro cell. In the scenario 3, on the other hand, the transmission/reception points created by the low power RRHs have a different cell ID from the macro cell. In the scenario 4, both the macro cell and its associated RRHs can act as transmission/reception points of a cell and are visible to the UE through the use of channel state information reference signals (or reference symbols) (CSI-RS).
The use of CSI-RS may especially aid MIMO transmissions in a CoMP architecture where each UE may need to estimate channel state information of multiple TPs. The CSI-RS constitute cell specific pilot symbols provided by an eNB that allow each UE to estimate CSI in the multi-TP CoMP environment independent from that used for pre-coding. Accordingly, the CSI-RSs were introduced in LTE release 10 to facilitate a given UE acquiring channel state information (CSI) in such MIMO environments. The reported CSI generally includes channel quality indicator (CQI), precoding matrix indicator (PMI), and/or rank indicator (RI) information. In particular, in a CoMP communications scheme, a UE may measure CSI-RSs transmitted from adjacent transmission points when the UE is located at a cell edge.
The eNodeB (or eNB) can configure a given UE to report CSI for the most suitable transmission/reception point (hereinafter simply referred to as a transmission point or “TP”) through radio resource control (RRC) configuration/reconfiguration. In a CoMP scenario in which the eNB is to configure only one CSI report instance for one UE, the UE may report CSI for one or more TPs. This may consist of one CSI-RS pattern and may maximize certain performance matrices, such as the UE's throughput. Thus, when a UE is mobile within a given cell, RRC reconfiguration may be desirable if the TP(s) for which the UE is currently reporting channel quality information (CQI) are no longer the best TP(s) for serving the UE.
It is with respect to these and other considerations that the present improvements have been needed.